Reverse dual positive airway pressure challenges for breathing disorder diagnostics

ABSTRACT

Systems and methods for classifying breathing disorders of subjects are based on the respiratory response to a change in a pressure level of a pressurized flow of breathable gas. The change presents a breathing challenge to a subject. The challenge may be limited to the inspiratory breathing phase. The inspiratory pressure level may be lower than the expiratory pressure level during challenges.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a Continuation application of U.S. National Phaseapplication under 35 U.S.C. § 371, Ser. No. 15/116,277, filed on Aug. 3,2016, which claims the benefit of International Application Serial No.PCT/IB2015/050632, filed on Jan. 28, 2015, which claims the benefit ofU.S. application Ser. No. 61/941631, filed on Feb. 19, 2014. Theseapplications are hereby incorporated by reference herein.

BACKGROUND 1. Field

The present disclosure pertains to systems and methods for classifyingbreathing disorders of subjects. In particular, the present disclosurepertains to adjusting the pressure level of a pressurized flow ofbreathable gas and determining a classification based on the respiratoryresponse by a subject.

2. Description of the Related Art

Some types of respiratory therapy involve the delivery of a pressurizedflow of breathable gas to the airway of a subject. A therapy session may(be intended to) span eight or more hours, and may (be intended to)coincide and/or overlap, at least in part, with a subject's daily and/ornightly sleeping period. A subject's comfort during a therapy session isa useful factor in therapy adoption rates and/or therapy success rates.

SUMMARY

Accordingly, one or more embodiments of the present disclosure provide asystem that includes a pressure generator, one or more sensors, and oneor more physical processors. The pressure generator is configured toprovide a pressurized flow of breathable gas at a pressure level to anairway of a subject. The one or more sensors are configured to generateoutput signals conveying information related to breathing of thesubject. The one or more physical processors configured to obtain arecommended respiratory therapy regimen for the subject that includes arecommended inspiratory positive airway pressure level and a recommendedexpiratory positive airway pressure level; determine one or more timingparameters related to the breathing of the subject based on thegenerated output signals; control the pressurized flow in accordancewith the recommended respiratory therapy regimen such that the pressurelevel of the pressurized flow corresponds to the recommended inspiratorypositive airway pressure (IPAP) level during inspirations and thepressure level of the pressurized flow corresponds to the recommendedexpiratory positive airway pressure (EPAP) level during expirations,wherein control is based on the one or more timing parameters; reducethe pressure level of the pressurized flow with respect to therecommended IPAP level during inspiration for one or more breathingcycles; determine one or more breathing parameters of the subject basedon the generated output signals during the one or more breathing cycles;and determine a classification of a breathing disorder of the subjectbased on the determined one or more breathing parameters during the oneor more breathing cycles. In some embodiments, the pressure levelsduring inspiration and expiration may be adjusted upward and/or downwardindependently of each other.

It is yet another aspect of one or more embodiments of the presentdisclosure to provide a method to classify a breathing disorder of asubject. The method is implemented using a pressure generator, one ormore sensors, and one or more physical processors. The method includesproviding a pressurized flow of breathable gas at a pressure level to anairway of the subject; generating output signals conveying informationrelated to breathing of the subject; obtaining a recommended respiratorytherapy regimen for the subject that includes a recommended inspiratorypositive airway pressure (IPAP) level and a recommended expiratorypositive airway pressure (EPAP) level; determining one or more timingparameters related to the breathing of the subject based on thegenerated output signals; controlling the pressurized flow of breathablegas in accordance with the recommended respiratory therapy regimen suchthat the pressure level of the pressurized flow corresponds to therecommended IPAP level during inspirations and the pressure level of thepressurized flow corresponds to the recommended EPAP level duringexpirations, wherein control is based on the one or more timingparameters; reducing the pressure level of the pressurized flow withrespect to the recommended IPAP level during inspiration for one or morebreathing cycles; determining one or more breathing parameters of thesubject based on the generated output signals during the one or morebreathing cycles; and determining a classification of a breathingdisorder of the subject based on the determined one or more breathingparameters during the one or more breathing cycles.

It is yet another aspect of one or more embodiments to provide a systemconfigured to classify a breathing disorder of a subject. The systemincludes means for providing a pressurized flow of breathable gas at apressure level to an airway of the subject; means for generating outputsignals conveying information related to breathing of the subject; meansfor obtaining a recommended respiratory therapy regimen for the subjectthat includes a recommended inspiratory positive airway pressure leveland a recommended expiratory positive airway pressure level; means fordetermining one or more timing parameters related to the breathing ofthe subject based on the generated output signals; means for controllingthe pressurized flow of breathable gas in accordance with therecommended respiratory therapy regimen such that the pressure level ofthe pressurized flow corresponds to the recommended IPAP level duringinspirations and the pressure level of the pressurized flow correspondsto the recommended EPAP level during expirations, wherein operation ofthe means for controlling is based on the one or more timing parameters;means for reducing the pressure level of the pressurized flow withrespect to the recommended IPAP level during inspiration for one or morebreathing cycles; means for determining one or more breathing parametersof the subject based on the generated output signals during the one ormore breathing cycle; and means for determining a classification of abreathing disorder of the subject based on the determined one or morebreathing parameters during the one or more breathing cycles.

These and other aspects, features, and characteristics of the presentdisclosure, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a system to classify breathingdisorders, according to certain embodiments;

FIG. 2 illustrates a method to classify a breathing disorder of asubject, according to certain embodiments;

FIG. 3 illustrates a varying pressure level of a pressurized flow ofbreathable gas provided to a subject and further illustrates acorresponding flow rate of the subject that may be used to classify abreathing disorder according to certain embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As used herein, the singular form of “a”, “an”, and “the” include pluralreferences unless the context clearly dictates otherwise. As usedherein, the statement that two or more parts or components are “coupled”shall mean that the parts are joined or operate together either directlyor indirectly, i.e., through one or more intermediate parts orcomponents, so long as a link occurs. As used herein, “directly coupled”means that two elements are directly in contact with each other. As usedherein, “fixedly coupled” or “fixed” means that two components arecoupled to move as one while maintaining a constant orientation relativeto each other.

As used herein, the word “unitary” means a component is created as asingle piece or unit. That is, a component that includes pieces that arecreated separately and then coupled as a unit is not a “unitary”component or body. As employed herein, the statement that two or moreparts or components “engage” one another shall mean that the parts exerta force against one another either directly or through one or moreintermediate parts or components. As employed herein, the term “number”shall mean one or an integer greater than one (i.e., a plurality).

Directional phrases used herein, such as, for example and withoutlimitation, top, bottom, left, right, upper, lower, front, back, andderivatives thereof, relate to the orientation of the elements shown inthe drawings and are not limiting upon the claims unless expresslyrecited therein.

A subject's comfort during a therapy session may be a useful and/orimportant factor in therapy adoption rates and/or therapy success rates.Due to poor comfort, many subjects do not like (CPAP) therapy. Forexample, approximately 50% of subjects quit using CPAP therapy withinseveral months. It is generally held that 50% of the affected populationdoes not choose to seek medical care for Sleep Disorder Breathing (SDB)in the first place, with one of the main reasons being that the CPAP isconsidered an unacceptable treatment. There are a growing number ofalternative treatments that are viewed more favorably by theunder-served, but the issue is that virtually all of those alternativesonly treat specific segments of the patient population, due to the factthat these alternatives treat only specific causes of obstruction orairway instability. These alternatives may be successful responsive to agiven subject having success with treating their particular SBD rootcause, in addition to the general use of the intervention beingacceptable to them. By virtue of this disclosure, subjects may beincreasingly confident in knowing that the treatment will work in aparticular case, since the particular root cause may be determine and/orclassified. Once a root cause has been determined and/or classified,more viable options may be provided to a subject that are customized forthe individual subject's problems and preferences.

FIG. 1 schematically illustrates a system 100 configured to classifybreathing disorders for subjects, for example a subject 106 having anairway. Classification of breathing disorders, in particular by thesource or (root) cause of a disorder, may enable selection of a properintervention and/or treatment. Classifying subjects or patients (basedon the type of breathing disorder) may be referred to as phenotypingpatients. A subject's phenotype may determine (and/or be used todetermine) the interventions and type of care most likely and/or bestsuited to treat their condition or disease.

System 100 may be implemented as, integrated with, and/or operating inconjunction with a respiratory device that provides a pressurized flowof breathable gas along a flow path to subject 106. System 100 mayinclude one or more of a pressure generator 140, a subject interface180, one or more sensors 142, an electronic storage 130, a userinterface 120, a processor 110, a therapy component 111, a timingcomponent 112, a control component 113, a challenge component 114, abreathing parameter component 115, a classification component 116, arelief component 117, a stability component 118, and/or othercomponents. System 100 may be configured to provide respiratory therapyto subject 106.

Pressure generator 140 of system 100 in FIG. 1 may be integrated,combined, or connected with a ventilator and/or (positive) airwaypressure device (PAP/CPAP/BiPAP®/etc.) and configured to provide apressurized flow of breathable gas for delivery to the airway of subject106, e.g. via one or more subject interfaces 180. Subject interface 180may sometimes be referred to as a delivery circuit.

As depicted in FIG. 1, pressure generator 140 fluidly communicates withsubject interface 180. Subject interface 180 fluidly communicates, via asubject interface appliance 184, with the airway of subject 106. Theconfiguration of various components in FIG. 1 is not intended to limitthe scope of the described technology in any way. For example, in someembodiments, system 100 may include a humidifier and/or interfaceheating system disposed between pressure generator 140 and subject 106.

Respiratory therapy may be implemented as pressure control, pressuresupport, volume control, and/or other types of support and/or control.For example, to support inspiration, the pressure of the pressurizedflow of breathable gas may be adjusted to an inspiratory positive airwaypressure (interchangeably referred to as inspiratory pressure, IPAP, orIPAP level). Alternatively, and/or simultaneously, to supportexpiration, the pressure and/or flow of the pressurized flow ofbreathable gas may be adjusted to an expiratory positive airway pressure(interchangeably referred to as expiratory pressure, EPAP, or EPAPlevel). Other schemes for providing respiratory support and/orventilation through the delivery of the pressurized flow of breathablegas are contemplated. Subject 106 may but need not initiate one or morephases of respiration. Devices that provide different IPAP and EPAPlevels may be referred to as dual (positive) airway pressure devices. Anexample of a dual positive airway pressure device is a BiPAP® device.Typically for dual positive airway pressure devices, the IPAP level ishigher than the EPAP level. As used herein, providing a lower IPAP levelthan EPAP level may be referred to as reverse dual positive airwaypressure, since it is the opposite of typical dual positive airwaypressure.

System 100 may be configured to adjust and/or maintain levels ofpressure, flow, humidity, velocity, acceleration, and/or otherparameters of the humidified, pressurized flow of breathable gas. One ormore adjustments may occur in substantial synchronization with thebreathing cycle of the subject. In some embodiments, one or moreoperating levels (e.g. pressure, volume, etc.) are adjusted on arelatively ongoing manner (e.g., each breath, every few breaths, everyfew seconds, etc.) during an individual session of respiratory therapyto titrate the therapy. Alternatively, and/or simultaneously,adjustments to one or more operating levels of system 100 and/or anycomponent thereof may be made more intermittently and/or between therapysessions rather than during a particular therapy session.

Pressure generator 140 is configured to provide and/or deliver apressurized flow of breathable gas to the airway of subject 106, e.g.via one or more subject interfaces 180. Subject interface 180 mayinclude a conduit 182 and/or a subject interface appliance 184. Asdepicted in FIG. 1, subject interface 180 may include a conduit 182.Conduit 182 may include a flexible length of hose, or other conduit. Asdepicted in FIG. 1, conduit 182 may place subject interface appliance184 in fluid communication with pressure generator 140. Conduit 182 mayform a flow path through which the pressurized flow of breathable gas iscommunicated between subject interface appliance 184 and pressuregenerator 140.

Subject interface appliance 184 of system 100 in FIG. 1 is configured todeliver the pressurized flow of breathable gas to subject 106, e.g. tothe airway of subject 106. Subject interface appliance 184 may beconfigured to reduce and/or inhibit condensation from forming along thepath of delivery of a pressurized flow of breathable gas to subject 106.Subject interface appliance 184 may include any appliance suitable forthe described function.

In some embodiments, pressure generator 140 is a dedicated ventilationdevice and subject interface appliance 184 is configured to be removablycoupled with another interface appliance being used to deliverrespiratory therapy to subject 106. For example, subject interfaceappliance 184 may be configured to engage with and/or be inserted intoan endotracheal tube, a tracheotomy portal, and/or other interfaceappliances. In one embodiment, subject interface appliance 184 isconfigured to engage the airway of subject 106 without an interveningappliance. In this embodiment, subject interface appliance 184 mayinclude one or more of an endotracheal tube, a nasal cannula, atracheotomy tube, a nasal mask, a nasal/oral mask, a full-face mask, atotal facemask, and/or other interface appliances that communicate aflow of gas with an airway of a subject. The present disclosure is notlimited to these examples, and contemplates delivery of the pressurizedflow of breathable gas to subject 106 using any subject interface.

Subject interface appliance 184 may be configured to be removablycoupled to conduit 182. Subject interface appliance 184 may beconfigured to be installed in the face of subject 106 to place theairway of subject 106 in fluid communication with conduit 182 fordelivery of a pressurized flow of breathable gas through conduit 182 tothe airway of subject 106.

Electronic storage 130 of system 100 in FIG. 1 comprises physicalelectronic storage media that electronically stores information, e.g.digital information. The electronic storage media of electronic storage130 may include one or both of system storage that is providedintegrally (i.e., substantially non-removable) with system 100 and/orremovable storage that is removably connectable to system 100 via, forexample, a port (e.g., a USB port, a FireWire port, etc.) or a drive(e.g., a disk drive, etc.). Electronic storage 130 may include one ormore of optically readable storage media (e.g., optical disks, etc.),magnetically readable storage media (e.g., magnetic tape, magnetic harddrive, floppy drive, etc.), electrical charge-based storage media (e.g.,EPROM, EEPROM, RAM, etc.), solid-state storage media (e.g., flash drive,etc.), and/or other electronically readable storage media. Electronicstorage 130 may store software algorithms, information determined byprocessor 110, information received via user interface 120, and/or otherinformation that enables system 100 to function properly. For example,electronic storage 130 may record or store one or more gas and/orrespiratory parameters (as discussed elsewhere herein), and/or otherinformation. Electronic storage 130 may be a separate component withinsystem 100, or electronic storage 130 may be provided integrally withone or more other components of system 100 (e.g., processor 110).

User interface 120 of system 100 in FIG. 1 is configured to provide aninterface between system 100 and a user (e.g., a user 108, subject 106,a caregiver, a therapy decision-maker, etc.) through which the user canprovide information to and receive information from system 100. Thisenables data, results, and/or instructions and any other communicableitems, collectively referred to as “information,” to be communicatedbetween the user and system 100. An example of information that may beconveyed to user 108 is a report detailing operational settings ofpressure generator 140 as selected and/or preferred by subject 106. Anexample of information that user 108 or subject 106 may provide tosystem 100 is a target temperature or target pressure level duringrespiratory therapy. Examples of interface devices suitable forinclusion in user interface 120 include a keypad, buttons, switches, akeyboard, knobs, dials, levers, a display screen, a touch screen,speakers, a microphone, an indicator light, an audible alarm, and aprinter. Information may be provided to user 108 or subject 106 by userinterface 120 in the form of auditory signals, visual signals, tactilesignals, and/or other sensory signals.

It is to be understood that other communication techniques, eitherhard-wired or wireless, are also contemplated herein as user interface120. For example, in one embodiment, user interface 120 may beintegrated with a removable storage interface provided by electronicstorage 130. In this example, information is loaded into system 100 fromremovable storage (e.g., a smart card, a flash drive, a removable disk,etc.) that enables the user(s) to customize the embodiment of system100. Other exemplary input devices and techniques adapted for use withsystem 100 as user interface 120 include, but are not limited to, anRS-232 port, RF link, an IR link, modem (telephone, cable, Ethernet,internet or other). In short, any technique for communicatinginformation with system 100 is contemplated as user interface 120.

One or more sensors 142 of system 100 in FIG. 1 are configured togenerate output signals conveying information related to the breathingof subject 106 and/or to physiological parameters of subject 106,including but not limited to respiratory parameters. One or more sensors142 may be in fluid communication with conduit 182, subject interfaceappliance 184, and/or other components of system 100. In someembodiments, the generated output signals may convey measurementsrelated to parameters of the flow of breathable gas within system 100.By way of non-limiting example, the parameters may include respiratoryparameters, timing parameters, physiological parameters, environmentalparameters, medical parameters, and/or other parameters.

The parameters may include one or more of (peak) flow, flow rate,volume, leak flow, leak volume, (airway) pressure, barometric pressure,temperature, humidity, velocity, acceleration, and/or other parameters.The respiratory parameters may include respiratory timing parameters,including but not limited to parameters related to transitions inbreathing between inhalations/inspirations and exhalations/expirations,transition time from peak inhalation flow rate to peak exhalation flowrate and/or vice versa, transitions moments or durations, breathingperiod, respiratory rate, inspiration time or period, expiration time orperiod, start and/or end in inspiratory phases, start and/or end ofexpiratory phases, and/or other respiratory timing parameters.

Environmental parameters may be related to one or more of the parametersof electromagnetic radiation, various temperatures, humidity levels,and/or other environmental parameters, which may be related toenvironmental conditions near system 10 or near subject 106. One or moremedical parameters may be related to monitored vital signs of subject106, physiological parameters of subject 106, and/or other medicalparameters of subject 106.

One or more sensors 142 may generate output signals conveyinginformation related to parameters associated with the state and/orcondition of an airway of subject 106, the breathing of subject 106, thebreathing rate of subject 106, the gas delivered to subject 106, thecomposition, temperature, and/or humidity of the gas delivered tosubject 106, the delivery of the gas to the airway of subject 106,and/or a respiratory effort by the subject. For example, a parameter maybe related to a mechanical unit of measurement of a component ofpressure generator 140 (or of a device that pressure generator 140 isintegrated, combined, or connected with) such as valve drive current,rotor speed, motor speed, blower speed, fan speed, or a relatedmeasurement that may serve as a proxy for any of the previously listedparameters through a previously known and/or calibrated mathematicalrelationship. Resulting signals or information from one or more sensors142 may be transmitted to processor 110, user interface 120, electronicstorage 130, and/or other components of system 100. This transmissionmay be wired and/or wireless.

Physiological parameters may be related to patient movement,cardio-vascular function, pulmonary function, central nervous systemfunction, local motor-neuron function, mechanical motion of the body orits organs, and/or other parameters. In some embodiments, sensor 142 mayinclude sensors to monitor subject 106, including, but not limited to,sensors to measure polysomnography, electro-encephalography (EEG),electro-oculography (EOG), electromyography (EMG), electrocardiography(ECG), and/or sensors for other types of monitoring.

The illustration of sensor 142 including one member in FIG. 1 is notintended to be limiting. The illustration of a sensor 142 at or nearsubject interface appliance 184 is not intended to be limiting, thoughthat location may be preferred in some embodiments to provide feedbackand/or information regarding the current flow rate of the pressurizedflow of breathable gas being delivered to the airway of subject 106. Forexample, this current flow rate may function as feedback for a targetflow rate for controlling pressure generator 140.

Processor 110 of system 100 in FIG. 1 is configured to provideinformation processing capabilities in system 100. As such, processor110 includes one or more of a digital processor, an analog processor, adigital circuit designed to process information, an analog circuitdesigned to process information, and/or other mechanisms forelectronically processing information. Although processor 110 is shownin FIG. 1 as a single entity, this is for illustrative purposes only. Insome embodiments, processor 110 includes a plurality of processingunits.

As is shown in FIG. 1, processor 110 is configured to execute one ormore computer program components. The one or more computer programcomponents include one or more of therapy component 111, timingcomponent 112, control component 113, challenge component 114, breathingparameter component 115, classification component 116, relief component117, stability component 118, and/or other components. Processor 110 maybe configured to execute components 111-118 by software; hardware;firmware; some combination of software, hardware, and/or firmware;and/or other mechanisms for configuring processing capabilities onprocessor 110.

It should be appreciated that although components 111-118 areillustrated in FIG. 1 as being co-located within a single processingunit, in embodiments in which processor 110 includes multiple processingunits, one or more of components 111-118 may be located remotely fromthe other components. The description of the functionality provided bythe different components 111-118 described herein is for illustrativepurposes, and is not intended to be limiting, as any of components111-118 may provide more or less functionality than is described. Forexample, one or more of components 111-118 may be eliminated, and someor all of its functionality may be provided by other ones of components111-118. Note that processor 110 may be configured to execute one ormore additional components that may perform some or all of thefunctionality attributed below to one of components 111-118. In someembodiments, some or all of the described functionality of an individualcomputer program component may be incorporated, shared, embedded, and/orintegrated into one or more other computer program components orelsewhere within system 100.

Therapy component 111 may be configured to obtain a respiratory therapyregimen for subject 106. For example, the obtained respiratory therapyregimen may be a recommended respiratory therapy regimen. In someembodiments, therapy component 111 may be configured to obtain arespiratory therapy regimen from a user (such as subject 106 and/or user108, a caregiver, a therapy decision-maker, etc.). In some embodiments,therapy component 111 may be configured to obtain and/or receive arespiratory therapy regimen that may be determined and/or devisedalgorithmically based on, at least, subject-specific information. Insome embodiments, therapy component 111 may be configured to determine arecommended respiratory therapy regimen, e.g. based on, at least,subject-specific information. Additional information that may be used todetermine a respiratory therapy regimen may be obtained from and/orthrough a knowledge base (or knowledge database).

In some embodiments, the obtained respiratory therapy regimen mayinclude a recommended inspiratory positive airway pressure (IPAP) level,a recommended expiratory positive airway pressure (EPAP) level, and/orother recommended pressure levels. In some embodiments, the recommendedpressure levels may be determined and/or selected to maintain breathingby subject 106 that is free of apneas, hypopneas, and/or otherrespiratory events, or at least expected to be so. In some embodiments,the recommended pressure levels may be determined and/or selected suchthat the airway of subject 106 is deemed and/or expected to be stableand/or unobstructed. In some embodiments, the recommended pressurelevels may be selected to be below a prescribed continuous positiveairway pressure (CPAP) level to treat apnea and/or other respiratoryevents. Determinations and/or selections by therapy component 111 may bebased on determinations by other computer program components, includingbut not limited to stability component 118.

Timing component 112 may be configured to determine one or more timingparameters related to the breathing of subject 106, including but notlimited to respiratory timing parameters described elsewhere in thisdisclosure. For example, timing parameters may include the moment ofonset of inspiration, the moment of onset of expiration, (estimated ormeasured) duration or period of inspiration, (estimated or measured)duration or period of expiration, pause between inspiration andexpiration and/or vice versa, transition time from peak inhalation flowrate to peak exhalation flow rate and/or vice versa, start and/or end ininspiratory phases, start and/or end of expiratory phases, and/or otherrespiratory timing parameters, combinations of respiratory timingparameters, and/or parameters based thereon.

Control component 113 may be configured to control operation of system100, pressure generator 140, and/or related components. Controlcomponent 113 may be configured to perform control functionality inmultiple modes of operation. Control component 113 may be configured tocontrol transitions between different modes of operation. Controlcomponent 113 may be configured to determine what the current mode ofoperation is, and/or share such information with other components ofsystem 100. Control component 113 may be configured to control pressuregenerator 140 such that one or more gas parameters of the pressurizedflow of breathable gas are varied over time in accordance with arespiratory therapy regimen. Control component 113 may be configured tocontrol pressure generator 140 to provide the pressurized flow ofbreathable gas at inhalation pressure levels (e.g. the recommended IPAPlevel) during inhalation phases, and at exhalation pressure levels (e.g.the recommended EPAP level) during exhalation phases. For example, afirst mode may correspond to providing challenges to subject 106, asdescribed elsewhere in this disclosure. A second mode of operation maycorrespond to providing relief to subject 106 after a particularobstruction or other respiratory event has occurred. Other modes ofoperation are envisioned within the scope of this disclosure.

Parameters determined by other computer program components and/orreceived through one or more sensors 142 may be used by controlcomponent 113, e.g. in a feedback manner, to adjust one or more therapymodes/settings/operations of system 100. Alternatively, and/orsimultaneously, signals and/or information received through userinterface 120 may be used by control component 113, e.g. in a feedbackmanner, to adjust one or more therapy modes/settings/operations ofsystem 100. Control component 113 may be configured to time itsoperations relative to the transitional moments in the breathing cycleof a subject, over multiple breath cycles, and/or in any other relationto any detected occurrences or determinations by timing component 112.

Challenge component 114 may be configured to adjust one or more pressurelevels of the pressurized flow of breathable gas being delivered tosubject 106. In some embodiments, the provided pressure levels duringinspiration and expiration may be adjusted upward and/or downwardindependently of each other. For example, challenge component 114 may beconfigured to reduce the inspiratory pressure level to be below therecommended IPAP level, for one or more breathing cycles. In someembodiments, the reduced inspiratory level may be lower than therecommended and/or actually provided expiratory pressure level. In someembodiments, a subject may be initially titrated to a particular CPAPlevel or two particular BiPAP levels that may enable the subject tobreathe normally (i.e. in a eupneic state, or a state of being treated),for example as characterized by the subject's body exhibitingcompensatory functions at a minimum level of activity, e.g. removing thebody's need to overcome a challenge, obstruction, condition, and/ordisease. A set of one or more breathing cycles for which the inspiratorypressure level is reduced may be referred to as a challenge, since thesubject will need to compensate in response. The response to theadjustment, e.g. to the reduced IPAP level, may be indicative of a typeof obstruction, and/or may be used as a basis for a classification byclassification component 116. Subjects having different types ofbreathing disorders may respond differently to certain challenges. Insome embodiments, the response may be indicative of the airwayreactivity to changes in lung volume and/or airway pressure. By virtueof separate and individual pressure control for the respiratory phases,interaction between the respiratory phases may be assessed.

In some embodiments, challenge component 114 may be configured toprovide a set of challenges, e.g. such that subsequent challenges havedifferent levels of inspiratory pressure levels. In some embodiments,the inspiratory pressure level may be repeatedly reduced throughsubsequent challenges until a particular condition occurs. Theparticular condition may include a timing parameter and/or breathingparameter breaching a particular threshold. In some embodiments, theparticular condition may be a determination that the stability of theairway has been compromised, e.g. through an obstruction, an arousal, atype of apnea, hypopnea, or other respiratory event, a type of sleepdisordered breathing (SDB), etc. In some embodiments, the particularcondition may be a determination that indicates airway instability. Asused herein, an onset of airway instability may be considered anindication of airway instability. Alternatively, and/or simultaneously,a determination that the stability of the airway has been compromisedmay be considered an indication of airway instability. The particularchallenge at which the particular condition occurs may be referred to asa point of interest for diagnostic purposes. For example, the IPAP levelmay be reduced gradually until some type of respiratory event (orobstruction in the airway of subject 106) occurs. The amount of reducedpressure needed to accomplish a particular occurrence may be used as aparameter by other computer program components, including but notlimited to classification component 116. The IPAP level may be reducedtemporarily, during challenges, to a pressure level below traditionaltreatment levels. For example, the reduced IPAP pressure level may beabout 1 cm-H₂O, about 2 cm-H₂ 0, about 3 cm-H₂O, about 4 cm-H₂O, about 5cm-H₂O, about 6 cm-H₂O, and/or another suitable pressure level.

In some embodiments, challenge component 114 may be configured toprovide one or more challenges with respect to a point of interest. Forexample, challenge component 114 may be configured to reduce the EPAPlevel at such a point in order to determine (one or more parametersindicative of) how subject 106 responds. For example, the response mayindicate a sensitivity of subject 106 to adjustments at or near aparticular point of interest. In some embodiments, the response bysubject 106 to a reduced EPAP level (in addition to a reduced IPAPlevel) may indicate severe airway instability (e.g. limited or no flowbeing measured). The particular EPAP adjustment that corresponds to suchan indication may be referred to as a point of interest for diagnosticpurposes. At various points of interest, adjustments to the inspiratorypressure and/or expiratory pressure may be made, in order to determine aresponse by subject 106. Responses by subject 106 to one or morepressure adjustments, in particular at or near points of interest, maybe used as a basis for a classification by classification component 116.

Breathing parameter component 115 may be configured to determine one ormore breathing parameters of subject 106, e.g. for the one or morebreathing cycles that correspond to a challenge. Determinations bybreathing component 115 may be based on output signals generated by oneor more sensors 142 and/or determinations by other computer programmodules. As used herein, breathing parameters may include gasparameters.

By way of non-limiting example, breathing parameters may include one ormore of (peak) flow, flow rate, leak flow, leak correction volume,(estimated) flow limitation during exhalation, residual volume, maximuminspiratory flow per breath, (tidal) volume, minute volume, inhalationor exhalation pressures, respiratory rate, breathing period, inhalationtime or period, exhalation time or period, respiration flow curve shape,transition time from inhalation to exhalation and/or vice versa,transition time from peak inhalation flow rate to peak exhalation flowrate and/or vice versa, respiration pressure curve shape, maximumproximal pressure drop (per breathing cycle and/or phase), change inpressure during the first 0.1 s of an inspiration, change in flow rateduring the last 0.1 s of an exhalation, (estimated) airway resistance,(estimated) airway compliance, gas temperature, gas humidity, gasvelocity, gas acceleration, gas composition (e.g. concentration(s) ofone or more constituents such as, e.g., CO₂), thermal energy dissipated,(intentional) gas leak, and/or other measurements related to the(pressurized) flow of breathable gas and/or other breathing parameters.In some embodiments, a breathing parameter may include ratios and/orother combinations of multiple other parameters. Some or all of thisfunctionality may be incorporated, shared, and/or integrated into othercomputer program components in system 100.

By way of non-limiting example, the one or more breathing parameters mayinclude a delay parameter that indicates a delay between an onset of aninspiratory phase that has a reduced pressure level and a change ininspiratory flow rate that corresponds to the onset of the inspiratoryphase. In some embodiments, the delay parameter may have a differentvalue for different types of challenges, depending on the type ofobstruction and/or breathing disorder. The delay parameter may beindicative of a particular type of obstruction and/or breathingdisorder. In some embodiments, the delay parameter may change betweendifferent challenges, which may be indicative of a particular type ofobstruction and/or breathing disorder. In some embodiments, the delayparameter may be substantially constant between different challenges,which may be indicative of another particular type of obstruction and/orbreathing disorder. In some embodiments, the delay parameter may be usedas a basis for a classification by classification component 116.

Classification component 116 may be configured to determineclassifications of breathing disorders of subjects. In some embodiments,a classification may pertain to a type of apnea, hypopnea, or otherrespiratory event. In some embodiments, a classification may pertain toa physical cause or a chemical cause, such as a particular chemicalbalance in the blood of subject 106. In some embodiments, aclassification may pertain to a type of sleep disordered breathing(SDB), including but not limited to snoring, upper airway resistancesyndrome (UARS), obstructive sleep apnea (OSA), and/or other types ofsleep disordered breathing. In some embodiments, a classification maypertain to different types of snoring, i.e. types of snoring caused byor at different sites of a subject. For example, a classification maypertain to obstructions located at different sites and/or caused bydifferent types of soft tissue, including but not limited to tongue,epiglottis, palate, esophageal flap, throat walls, airway walls,pharyngeal walls, and/or other bulk tissue or soft tissue. For example,a classification may distinguish between two or more different types ofobstructions. As used herein, the term obstruction may be interpreted toinclude collapses.

In some embodiments, determinations by classification component 116 maybe based on one or more determinations by breathing parameter component115, in particular for the one or more breathing cycles corresponding toa particular challenge. In some embodiments, a first determination bybreathing parameter component 115 for the first breathing cycle of aparticular challenge may be compared with a second determination bybreathing parameter component 115 for the second breathing cycle of theparticular challenge, and so forth.

In some embodiments, determinations by classification component 116 maybe based on one or more determinations by breathing parameter component115, in particular by comparing determinations for the one or morebreathing cycles corresponding to a first challenge with determinationfor the one or more breathing cycles corresponding to a second and/orthird challenge, and so forth. The classification component 116 may alsouse inputs from other systems, the subject's answers to questions,measured parameters, and/or ethnographic parameters in order to makedeterminations by classification component 116 more comprehensive,accurate, or precise.

Stability component 118 may be configured to determine whether theairway of subject 106 is stable and/or whether one or more parametersindicate airway instability. In some embodiments, stability component118 may be configured to determine whether (an onset of) an obstruction,a type of apnea, hypopnea, or other respiratory event, or a type ofsleep disordered breathing has occurred. For example, an onset of anarousal may be deemed to indicate airway instability. Alternatively,and/or simultaneously, stability component 118 may be configured todetermine whether stability of the airway has been restored, or whetheran obstruction, a type of apnea, hypopnea, or other respiratory event,or a type of sleep disordered breathing has been removed, reverted,and/or ceased. For example, a change in the one or more parameters thatpreviously indicated airway instability may indicate that the airwayinstability has been remedied. For example, the body of subject 106 mayreact to airway instability through an arousal, an onset of an arousal,a precursor to an arousal, and/or other physical reactions that may leadto an arousal.

Relief component 117 may be configured to adjust one or more pressurelevels of the provided pressurized flow of breathable gas, in particularin an attempt to restore stability of the airway of subject 106. Forexample, relief component 117 may be configured to increase the EPAPlevel and/or IPAP level responsive to a particular determination orcondition, including but not limited to stability of the airway ofsubject 106 having been compromised, and/or airway instability beingindicated by one or more parameters. The response to the adjustment,e.g. to an increased EPAP level, may be indicative of a type ofobstruction, and/or may be used as a basis for a classification byclassification component 116. Relief component 117 may be configured torepeatedly make adjustments, e.g. increase the EPAP level, until, e.g.,stability of the airway of subject 106 has been restored and/or airwayinstability is no longer indicated by the one or more parameters. Theparticular combination of inspiratory and expiratory levels at which theparticular condition occurs, e.g. onset of airway instability, may bereferred to as a point of interest for diagnostic purposes. The amountof adjusted pressure needed to accomplish this may be used as aparameter by other computer program components, including but notlimited to classification component 116. For example, the amount ofincreased EPAP pressure needed to resolve snoring may be different (e.g.typically lower) than the amount of increased EPAP pressure needed toprevent apneas (e.g. typically higher). Either amount of pressure maycorrespond to a separate point of interest, and either point of interestmay be used as a parameter by other computer program components,including but not limited to classification component 116.

At various points of interest, adjustments to the inspiratory pressureand/or expiratory pressure may be made, in order to determine a responseby subject 106. For example, at a point of severe airway instability,relief component 117 may be configured to increase the IPAP level toprovide relief. Responses by subject 106 to one or more pressureadjustments, in particular at or near points of interest, may be used asa basis for a classification by classification component 116.

By way of illustration, FIG. 3 illustrates a varying pressure level 30of a pressurized flow of breathable gas provided to a subject andfurther illustrates a corresponding flow rate 40 of the subject that maybe used to classify a breathing disorder. Periods 31, 33, 35, and 37correspond to inspirations or inspiration phases of breathing cycles.Periods 32, 34, and 36 corresponds to expirations or expiration phasesof breathing cycles. As depicted, the pressure levels during period 31and period 32 may be the same. The corresponding patient flow 41-42 forthe 31-32 periods show stable eupneic breathing. The combination of aperiod and the corresponding patient flow may be referred to as asegment, for example segment 31/41. Inspiratory flow rate 41, 43, 45 a,and 47 a correspond to periods 31, 33, 35, and 37, respectively.Expiratory flow rate 42, 44, and 46 correspond to period 32, 34, and 36,respectively. Period 33 corresponds to a first challenge for thesubject, in this case a reduced inspiratory pressure level, as depictedby the difference in pressure level between the pressure level in period31 and period 33. Period 33 and period 34 form a breathing cycle. Notethat the expiratory pressure level in period 34 is the same as in period32. The first challenge as depicted spans one breathing cycle, but thisis merely exemplary. One or more characteristics of inspiratory flowrate 43 (e.g. in comparison with inspiratory flow rate 41) may be usedto determine a classification as described elsewhere herein. In thisexample, the patient's airway is exhibiting some level of flowlimitation (i.e. flattening and broadening of the waveform in period 33,when compared to the waveform in period 31), because they are no longerexperiencing treatment pressure during inhalation on this breath, andsomething about their anatomy fails to keep the airway completely open.

Period 35 corresponds to a second challenge for the subject, in thiscase an even more reduced inspiratory pressure level compared to period33, as depicted by a difference 35 a in pressure level between period 33and period 35. The second challenge as depicted spans one breathingcycle, but this is merely exemplary. Inspiratory flow rate 45 aindicates the measured inspiratory flow rate that corresponds toinspiratory period 35. Expected inspiratory flow rate 45 b correspondsto the inspiratory flow rate as expected for a stable airway of thesubject. The difference between measured inspiratory flow rate 45 a andexpected inspiratory flow rate 45 b may indicate that the stability ofthe airway of the subject may have been compromised. One or morecharacteristics of this difference may be used to determine aclassification as described elsewhere herein. For example, thedifference may correspond to a lower-than-expected pressure inducedvolume. In other words, the second challenge was too great to maintain astable airway. To relieve the subject, the expiratory pressure duringperiod 36 may be increased compared to period 34, as indicated by adifference 36 a. Inspiratory flow rate 47 a indicates the measuredinspiratory flow rate that corresponds to inspiratory period 37.Expected inspiratory flow rate 47 b corresponds to the inspiratory flowrate as expected for a more stable airway of the subject; for instancein the 33/43 segment. The difference between measured inspiratory flowrate 47 a and expected inspiratory flow rate 47 b may indicate that thestability of the airway of the subject continues to be compromised tosome degree, but appears to have improved since the amplitude of flow ishigher than during segment 35/45, and the difference between measuredinspiratory flow rate 45 a and expected inspiratory flow rate 45 b isgreater than the difference between measured inspiratory flow 47 a andexpected inspiratory flow rate 47 b. One or more characteristics of thisdifference may be used to determine a classification as describedelsewhere herein. Note the different shape of measured inspiratory flow47 a compared to the measured inspiratory flow 45 a. Note that measuredinspiratory flow 47 a is higher than the measured inspiratory flow 45 a.In other words, the attempt to provide relief for the subject has notyet (e.g. fully) succeeded to restore stability of the airway of thesubject. For example, perhaps an additional increase of the expiratorypressure level would restore the stability. The response of theinspiratory pressure level to various adjustments of inspiratory and/orexpiratory pressure levels may indicate, for example in combination, aparticular classification of a breathing disorder. Note thatcharacteristics of differences between measured and expected flow rateare not limited to inspiratory phases, but may apply in a similar mannerto expiratory phases.

FIG. 2 illustrates a method 200 to classify a breathing disorder of asubject. The operations of method 200 presented below are intended to beillustrative. In certain embodiments, method 200 may be accomplishedwith one or more additional operations not described, and/or without oneor more of the operations discussed. Additionally, the order in whichthe operations of method 200 are illustrated in FIG. 2 and describedbelow is not intended to be limiting.

In certain embodiments, method 200 may be implemented in one or moreprocessing devices (e.g., a digital processor, an analog processor, adigital circuit designed to process information, an analog circuitdesigned to process information, a state machine, and/or othermechanisms for electronically processing information). The one or moreprocessing devices may include one or more devices executing some or allof the operations of method 200 in response to instructions storedelectronically on an electronic storage medium. The one or moreprocessing devices may include one or more devices configured throughhardware, firmware, and/or software to be specifically designed forexecution of one or more of the operations of method 200.

At an operation 202, a pressurized flow of breathable gas is provided ata pressure level to an airway of the subject. In some embodiments,operation 202 is performed by a pressure generator the same as orsimilar to pressure generator 140 (shown in FIG. 1 and describedherein).

At an operation 204, output signals are generated conveying informationrelated to breathing of the subject. In some embodiments, operation 204is performed by one or more sensors the same as or similar to one ormore sensors 142 (shown in FIG. 1 and described herein).

At an operation 206, a recommended respiratory therapy regimen isobtained for the subject that includes a recommended inspiratorypositive airway pressure (IPAP) level and a recommended expiratorypositive airway pressure (EPAP) level. In some embodiments, operation206 is performed by a therapy component the same as or similar totherapy component 111 (shown in FIG. 1 and described herein).

At an operation 208, one or more timing parameters are determinedrelated to the breathing of the subject based on the generated outputsignals. In some embodiments, operation 208 is performed by a timingcomponent the same as or similar to timing component 112 (shown in FIG.1 and described herein).

At an operation 210, the pressurized flow of breathable gas iscontrolled in accordance with the recommended respiratory therapyregimen such that the pressure level of the pressurized flow correspondsto the recommended IPAP level during inspirations and the pressure levelof the pressurized flow corresponds to the recommended EPAP level duringexpirations. Control is based on the one or more timing parameters. Insome embodiments, operation 210 is performed by a control component thesame as or similar to control component 113 (shown in FIG. 1 anddescribed herein).

At an operation 212, the pressure level of the pressurized flow isreduced with respect to the recommended IPAP level during inspirationfor one or more breathing cycles. In some embodiments, operation 212 isperformed by a challenge component the same as or similar to challengecomponent 114 (shown in FIG. 1 and described herein).

At an operation 214, one or more breathing parameters of the subject aredetermined based on the generated output signals during the one or morebreathing cycles, and. In some embodiments, operation 214 is performedby a breathing parameter component the same as or similar to breathingparameter component 115 (shown in FIG. 1 and described herein).

At an operation 216, a classification of a breathing disorder of thesubject is determined based on the determined one or more breathingparameters during the one or more breathing cycles. In some embodiments,operation 216 is performed by a classification component the same as orsimilar to classification component 116 (shown in FIG. 1 and describedherein).

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word “comprising” or “including”does not exclude the presence of elements or steps other than thoselisted in a claim. In a device claim enumerating several means, severalof these means may be embodied by one and the same item of hardware. Theword “a” or “an” preceding an element does not exclude the presence of aplurality of such elements. In any device claim enumerating severalmeans, several of these means may be embodied by one and the same itemof hardware. The mere fact that certain elements are recited in mutuallydifferent dependent claims does not indicate that these elements cannotbe used in combination.

Although the disclosure has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the disclosure is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present disclosure contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

1. A pressure support system configured to provide pressure support toan airway of a subject, the system comprising: a pressure generatorconfigured to provide a pressurized flow of breathable gas at a pressurelevel to the airway of the subject; a subject interface configured toconduct the pressurized flow of breathable gas to the airway of thesubject, the subject interface including an interface applianceconfigured to removably engage the airway of the subject; one or moresensors in fluid communication with the subject interface and configuredto generate output signals conveying information related to breathing ofthe subject; and one or more physical processors configured to: receivea recommended inspiratory positive airway pressure (IPAP) level and arecommended expiratory positive airway pressure (EPAP) level; controlthe pressure generator based on the output signals to generate thepressurized flow such that the pressure level of the pressurized flowcorresponds to the recommended IPAP level during inspirations of thesubject and the pressure level of the pressurized flow corresponds tothe recommended EPAP level during expirations of the subject; controlthe pressure generator to repeatedly reduce the pressure level of thepressurized flow with respect to the recommended IPAP level duringinspiration for one or more breathing cycles until the output signalsindicate airway instability of the subject; determine a reduced amountof the pressure level resulting from the repeated reduction that causedthe airway instability based on the generated output signals during theone or more breathing cycles; and determine a classification of abreathing disorder of the subject based on the reduced amount of thepressure level that caused the airway instability.
 2. The system ofclaim 1, wherein the one or more physical processors are configured suchthat the repeated reducing comprises: reducing the pressure level duringa first inspiration to a first reduced level and during a secondinspiration to a second reduced level, wherein the second inspiration issubsequent to the first inspiration, determining a first breathingparameter during the first inspiration and a second breathing parameterduring the second inspiration, and determining a difference between thefirst breathing parameter and the second breathing parameter, andwherein the classification is further based on the determineddifference.
 3. The system of claim 1, wherein the one or more physicalprocessors are further configured to: determine an inspiratory flow rateduring one or more inspirations that have the recommended IPAP level,determine a second inspiratory flow rate during the one or morebreathing cycles with the reduced pressure level, and further determinethe classification of the breathing disorder of the subject based on achange between the inspiratory flow rate and the second inspiratory flowrate.
 4. The system of claim 1, wherein the one or more physicalprocessors are further configured to: repeatedly increase the pressurelevel of the pressurized flow with respect to the recommended EPAP levelduring expirations for one or more breathing cycles; and determinewhether stability of the airway has been restored based on the generatedoutput signals, wherein the classification of the breathing disorder ofthe subject is further based on an amount the pressure level isincreased during expirations to restore the stability of the airway. 5.A method for providing pressure support to an airway of a subject, themethod being implemented using a pressure generator that provides apressurized flow of breathable gas at a pressure level to an airway ofthe subject, a subject interface, one or more sensors in fluidcommunication with the subject interface, and one or more physicalprocessors, the method comprising: generating, with the pressuregenerator, a pressurized flow of breathable gas at a pressure level fordelivery to the airway of the subject; conducting, with the subjectinterface, the pressurized flow of breathable gas to the airway of thesubject, the subject interface including an interface applianceconfigured to removably engage the airway of the subject; generating, bythe one or more sensors, output signals conveying information related tobreathing of the subject; receiving, with the one or more physicalprocessors, a recommended inspiratory positive airway pressure (IPAP)level and a recommended expiratory positive airway pressure (EPAP)level; controlling, with the one or more physical processors, thepressure generator based on the output signals to generate thepressurized flow of breathable gas such that the pressure level of thepressurized flow corresponds to the recommended IPAP level duringinspirations of the subject and the pressure level of the pressurizedflow corresponds to the recommended EPAP level during expirations of thesubject; repeatedly reducing, by controlling the pressure generator withthe one or more physical processors, the pressure level of thepressurized flow with respect to the recommended IPAP level duringinspiration for one or more breathing cycles until the output signalsindicate airway instability of the subject; determining, with the one ormore physical processors, a reduced amount of the pressure levelresulting from the repeated reduction; and determining, with the one ormore physical processors, a classification of a breathing disorder ofthe subject based on the reduced amount of the pressure level thatcaused the airway instability.
 6. The method of claim 5, whereinrepeatedly reducing the pressure level includes: reducing the pressurelevel during a first inspiration to a first reduced level; reducing thepressure level during a second inspiration to a second reduced level,wherein the second inspiration is subsequent to the first inspiration,determining a first breathing parameter during the first inspiration;determining a second breathing parameter during the second inspiration;and determining a difference between the first breathing parameter andthe second breathing parameter; and wherein determining theclassification is further based on the difference between the firstbreathing parameter and the second breathing parameter.
 7. The method ofclaim 5, further comprising: determining, with the one or more physicalprocessors, an inspiratory flow rate during one or more inspirationsthat have the recommended IPAP level, determining, with the one or morephysical processors, a second inspiratory flow rate during the one ormore breathing cycles with the reduced pressure level, and furtherdetermining the classification of the breathing disorder of the subjectbased on a change in between the inspiratory flow rate and the secondinspiratory flow rate.
 8. The method of claim 5, further comprising:repeatedly increasing, with the one or more physical processors and thepressure generator, the pressure level of the pressurized flow withrespect to the recommended EPAP level during expirations for one or morebreathing cycles determining, with the one or more physical processors,whether stability of the airway has been restored based on the generatedoutput signals; and further determining the classification of thebreathing disorder of the subject based on an amount the pressure levelis increased during expirations.
 9. A pressure support system configuredto provide pressure support to an airway of a subject, the systemcomprising: a pressure generator configured to provide a pressurizedflow of breathable gas at a pressure level to the airway of the subject;a subject interface configured to conduct the pressurized flow ofbreathable gas to the airway of the subject, the subject interfaceincluding an interface appliance configured to removably engage theairway of the subject; one or more sensors in fluid communication withthe subject interface and configured to generate output signalsconveying information related to breathing of the subject; and one ormore physical processors configured to: control the pressure generatorbased on the output signals to generate the pressurized flow at aninspiration pressure level during inspirations of the subject and at anexpiration pressure level during expirations of the subject; control thepressure generator to repeatedly reduce the pressure level of thepressurized flow from the inspiration pressure level during successiveinspirations of the subject, until the output signals indicate airwayinstability of the subject; determine, based on the output signals, areduced amount of the pressure level resulting from the repeatedreduction that caused the airway instability; and determine aclassification of a breathing disorder of the subject based on thereduced amount of the pressure level that caused the airway instability.10. The pressure support system of claim 9, wherein the one or morephysical processors are further configured to: determine a firstinspiratory flow rate during a first inspiration of the subject;determine a second inspiratory flow rate during a second inspiration ofthe subject, the pressure level of the pressurized flow of breathablegas being lower during the second inspiration relative to the firstinspiration, and further determine the classification of the breathingdisorder of the subject based on a difference between the firstinspiratory flow rate and the second inspiratory flow rate.
 11. Thepressure support system of claim 10, wherein the one or more physicalprocessors are configured such that the difference between the firstinspiratory flow rate and the second inspiratory flow rate is adifference in a shape of an inspiratory flow rate curve for the secondinspiration of the subject relative to the first inspiration of thesubject.
 12. The pressure support system of claim 9, wherein the one ormore physical processors are further configured to: determine a delayparameter that indicates a delay between an onset of a given inspirationof the subject and a change in an inspiratory flow rate that correspondsto the onset of the given inspiration of the subject; and furtherdetermine the classification of the breathing disorder of the subjectbased on the delay parameter.
 13. The pressure support system of claim12, wherein the one or more physical processors are configured such thatthe onset of the given inspiration occurs at a moment in time when animmediately previous exhalation of the subject ends, and wherein thechange in the inspiratory flow rate occurs subsequent to the end of theimmediately previous inhalation.